Dental amalgam alloy



Patented May 5, 1942 2,281,991 I DENTAL AMALGAM ALLOY Paul Poetschke, Bronxville, N. Y.

No Drawing.

Application April 27, 1938, Serial No. 204,564

' 1 Claim. (Cl. 75-173) This invention relates to dental amalgam alloys and method of making amalgams, and'is herein illustrated as embodied in dental amalgam alloys which are used for filling teeth and for making models. Such alloys consist principally of silver and tin with or without the addition of small quantities of copper and zinc and occasionally small amounts of gold or othermetals.

The American Dental Association specification for dental amalgam alloys for filling teeth (Journal of the American Dental Association, April 1934, page 660) requires that alloys for filling teeth contain not less than 65% of silver, not less than 25% of tin; not more than 6% of copper and not more than 2% of zinc. After amalgamation with mercury in accordance with instrucsultant amalgam shall comply with certain physical tests-,namely:

A. The amalgam must expand between 3 and f 39% of tin and 1% of zinc showed a contraction of 40 microns,,a flow of 32% and a crushing strength of 42,000 lbs. in one day and 45,000 lbs. in five days. Such alloys are used, notwithstanding their enormous shrinkage, because the amalgam produced is slow setting and thus is easy to manipulate when packing a number of impressions with a single mix of amalgam.

To obviate this shrinkage, model alloys containing 67% of silver, 27% of tin, 5% of copper and 1% of zinc, which yield a dental amalgam with practically'no shrinkage, have been available, but this type of amalgam alloy requires special care in manipulation because of its rapid tions recommended by the manufacturer, the re- 13 microns per centimeter at the end of 24 hours after amalgamation.

B. The amalgam must show not more than 4% shortening in length after 24 hours application of pressure (corresponding to 3,550 lbs. per

' square inch).

In former specifications there was also an ultimate compressive strength requirement of 35,500 lbs. per square inch. This requirement was abandoned because alloys which meet the requirements for chemical composition, volume change and flow would incidentally meet the requirement for crushing strength.

A report on thirty-one dental amalgam alloys (Journal of the American Dental Association,

' April, 1929, page 591) showed that alloys containing less than 64% of silver and more than 29% of tin would show excessive shrinkage and flow and low crushing strength. For instance,

, an alloy containing 44.0% of silver and 55.2% of tin showed a contraction of 16.5 microns and a crushing strength of 20,200 lbs. per square inch.

Another alloy containing 44.1% of silver and 51.0% of tin showed a contraction of 27 microns and a crushing strength of 25,000 lbs. per square inch. An alloy containing 54.8% of silver and 40.5% of tin showed a contraction of microns,

a flow of 25% and a crushing strength of 36,700 lbs. per square inch. However, an alloy contain ing 68.7% of silver and 26.1% of tin showed an expansion of 3.5 microns, a flow of 2.8% and a crushing strength of 54,500 lbs. per square inch. I

These examples are sufiicient to indicate that itv was then believed that alloys containing a higher percentage of silver and less tin had better physioal properties than those containing less silver I and more tin.

Most model alloys sold at the present time con setting qualities.

An alloy containing 54% of silver, 29% of tin, 16% of copper and 1% of zinc has also been available but the amalgam produced its rapid setting, and offers resistance to removal of surplusmercury so that it is difficult to pack more than one or two impressions, and unless great care is taken in removing surplus merciu'y, the models will sweat mercury and so contaminate the gold (of adjacent gold inlays) during subsequent polishing operations.

I have found that dental amalgam alloys of superior physical properties may be produced by a considerable increase in the copper and zinc content, such as has been hitherto thought to beimpossible of accomplishment and, by so do-- ing, I have been able to decrease enormously the percentage of silver required. For example, I have found that an alloy-composed of 39.61% of silver, 29.05% of tin, 23.34% of copper and 8.00% of zinc, having the metals present in,the molecular proportion AgsCusSnaZn, yields upon amalgamation an amalgam having a volume change of less than three microns, a flow of 1.5%, a crushing strength of 59,000 lbs. in one day and the extraordinary strength of 70,000 lbs. after five days hardening. This alloys yields an amalgam approximately 15% higher in crushing strength than that produced from the best silver alloys hitherto used for fillings and containing up to 70% of silver, and approximately 50% higher than amalgam produced from the slower setting model alloys containing around of silver.

I have found that this preferred comp sition yields amalgam free from the stated disadvantages, it being possible to pack eight or ten implasticity models, but it may also be used for filling teeth, especially deciduous teeth of children which are now often filled with copper amalgam. Its advantage over copper amalgam lies in its greater permanence and insolubility, greater strength, freedom from contraction, the fact that it is nontarnishable whereas copper amalgam tarnishes badly; that it provides more time for placement than high silver amalgams and hardens more rapidly than copper amalgam after the filling is completed.

It will be understood by those skilled in the art, that the essential qualities desired in a model alloy are reasonably retarded setting, to give ample packing time especially when a number of impressions must be packed from one mix, freedom from shrinkage, high strength and freedom from any tendency to sweat mercury." The preferred composition given fulfills these requirements.

For filling teeth, it is necessary to provide an adequate expansion. Owing to the fact that amalgam expands three times as much as tooth structure for the same change in temperature, and that an amalgam filling is subjected to a range of 41 F. to 131 F. in the mouth, it is necessary to compensate for a shrinkage of /2 microns due to differential contraction ,(see Technologic Paper 157, Bureau of Standards, and S. Mamlet, Dental Items of Interest, September, 1935). To this must be added a sumcient expansion to compensate for any'initial shrinkage due to chemical combination. This may amount to 5 microns. Thus an expansion of around microns is necessary to avoid leakage.

Most of the specification alloys now sold do not expand sufliciently to yield a tight filling because the limit of the specifications is obviously too low. It is known that silver alloys-having a silver and tin content within the specifications range may be made to expand more by light trituration duringamalgamation. It is impossible to control such manipulative expedients and, moreover, the crushing strength, packing quality, adaptation and smoothness of the amalgam is adverselyaffected by light trituration. With vigorous trituration, a smooth amalgam, adaptation and high crushing strength is secured but the amalgam shrinks or does not expand sufliciently.

I have found that it is possible to provide the necessary expansion of either the AgaCuaSmZn alloy or of the specification" alloy without ad-, versely affecting other properties of the resulting amalgam by adding to the comminuted silver alloy a predetermined amount of preformed amalgam. By the term preformed amalgam, I mean an amalgam usually the hardened amalgam, composed of granules or fine particles of amalgam formed by amalgamating a dental amalgam alloy with mercury, or formed by amalpedients in manipulation which are harmful to a other physical properties of the amalgam.

- increased considerably.

providing good packing quality,

gamating pure silver with mercury. Thus the comminuted hardened pre-formedalloy is rich in silver and mercury. By the addition of preformed comminuted amalgam to the comminuted silveralloy, I have found it possible to counterbalance the shrinkage of "amalgam and-to cause it to yield either a non-shrinking, non-expanding model amalgam or to provide any-desired degree of expansion. I may thus improve a filling amalgam which by itself shrinks .or does not expand sufficiently to yielda leakproof filling and give it any desired expansion without the need for ex- It is not necessary that the alloy be very close to the formula AgaCuzsmzn. Apparently an alloy including not over 54% silver and containing more than 18% copper, the balance being tin is likely to be useful as a dental alloy. Such an alloy is even superior if it contains zinc tin, preferably in an amount of 8% or more.

If the silver is reduced the copper is preferably One very satisfactory alloy was silver 38%, tin 30%, copper 24%, zinc 8%.

Some suitable preformed amalgams rich in silver and mercury are as follows, alpha, beta and gamma:

of the preformed amalgam brings the expansion within the requirements of the American Dental Association specifications. Thus, this dental amalgam alloy meets the physical tests for filling alloys demanded by that specification.

CHART l I MICRONS PER CENT COMPOSlTION ALLOY P-A crushing strength 2,000 lbs., and slightly raises the flow. It is seen that the slight lowering of crushing strength varies directly with the amount of the preformed amalgam which is added and that the flow increases slightly with increased amounts of preformed amalgam. Itis customary in packing models in dental offices and laboratories to leave such models harden overnight. They are, thus, allowed to harden for Alpha Beta Gamma Percent Percent Percent Mercury 37. 50

periods of anywhere between 16 and 24 hours. Curve B shows that the addition of of preformed amalgam, Gamma P-A, produces an amalgam that is absolutely neutral. The graph further shows that it is possible to have not only a non-shrinking, non-expanding amalgam but that it is also possible to have either expansion or contraction and thus provide amalgams which will compensate for volume changes in impression compounds and waxes which are used in conjunction with the technics required for providing dental restorations in the mouth. Referring back to Graph 1, it will be seen that even greater expansion can be provided to compensate for shrinkages in other material employed in making dental restorations. This is done by varying the composition of the preformed amalgam.

CHART 2 mcno NS PER CENT COMPOSITION Graph or Chart 3 shows the eifect produced by adding preformed amalgam, "Alpha P-Al to a standard high silver alloy which complies with the chemical and physical specifications of the American Dental Association. The untreated alloy A expands 4 /2 microns. The addition of 5% 01' preformed amalgam Alpha P-A increases the expansion to 14 microns. Thus, it is possible to increase the expansion 01' a regular specification alloy to the maximum limit rerruired by the specifications or beyond, without altering the crushing strength or materially afiecting the flow of the amalgam.

Graph or Chart 4 presents the same dental amalgam alloy as listed in A of Chart 3 to which varying quantities from 5 to 20% of pre-- formed amalgam, Beta P-A, have been added. It will be seen that each addition of the Beta P-A, preformed amalgam produces an increase in the expansion. It is also shown that there is a slight but regular decrease in the crushing strength and an increase in the flow as the amount of preformed amalgam is increased. Itis seen that composition E with 20% of Beta preformed amalgam reaches the maximum expansion demanded by the American Dental Association specifications and is within the limit prescribed for flow, and it also provides an amalgem with as high a crushing strength as most specification alloys.

Graph or Chart 5 shows the same high silver alloy A which appears in Charts 3 and 4. In this case, preformedamalgam, Gamma -P-A, was added in the quantities of 10 and 20%. While the preformed amalgam, Alpha" and "Beta" caused a regular increase in the expansion with increase in the amount of preformed amalgam, the Gamma preformed amalgam reaches its maximum expansion at 10% and an addition up to 20% actually reduces the expansion slightly under that produced by the 10%. The crushing strength and flow are but slightly affected.

CHART a u ICRONS PER CELNT COMFOSI'IION CHART 4 PER CE NT COMPOSITION N l DAY INCH DAYS

56000 sumo an 56000 woo as PER CENT COMPOSIT ON ssoco A considerable number of dental amalgam alloys which are sold in the open market as model alloys and fillin alloys and which show a contraction or an inadequate expansion are improved in the amount of expansion by the addition of comminuted preformed amalgam rich in silver and mercury.

It will be understood that the addition mm.

- minuted preformed amalgamwhether of the composition, Alpha, Beta or "Gamma" all rich in silver and mercury increases the expansion of any dental amalgam alloy containing silver whether it is of the class of alloys termed s1 ecifl'cation" alloys or whether it is of the class Graphs 1 and 2 is a new time of dental amalgam alloy of unusually low silver content which has properties hitherto unobtainable. By the additron thereto of preformed amalgam it is possible to produce low silver dental amalgam alloys for either filling purposes or for models which not only have the desired physical properties, but also have unusual manipulative characteristics.

It is possible to sell the comminuted hardened preformed alloyrich in silverand mercury separately or to sell the final alloy mixture ready for the addition of mercury to the mixture to form the amalgam.

Having thus described certain embodiments of the invention,,what is claimed is:

A dental alloy consisting of 100 parts of a mechanical mixture of two alloys, one being to parts of a comminuted silver alloy and the other being 20 to 5 parts of preformed hardened silver amalgam, the said 80 to 95 parts consisting '01 39.61% '00 68.50% silver, 4.70% to 23.34%

copper, 0.80% to 8.00% zinc and the balance tin; and said 20 to 5 parts consisting of a comminuted preformed hardened silver amalgam, rich in silver andmercury.

PAUL POETSCHKE. 

